1. Field of the Invention
The present invention relates generally to a rack and pinion steering assembly; and more specifically, to a self-sealing yoke assembly for supporting the rack and pinion of the steering assembly.
2. Description of Related Art
Modern automotive vehicle steering assemblies typically use a rack and pinion gear system that translates the rotational movement of the steering wheel into linear movement needed to turn the vehicle wheels. In general, a housing encloses a rack and pinion gear set. A steering shaft attaches to the pinion gear such that rotation of the steering wheel turns the pinion gear that correspondingly moves the rack. Tie rods connect the rack to the vehicle wheels such that movement of the rack turns the wheels. Most automotive vehicles utilize a power assisted rack and pinion steering system. Part of the power-assisted steering system assembly includes a cylinder with a piston in the middle wherein the piston connects to the rack. There are two fluid ports one on either side of the piston. Supplying higher-pressure fluid to one side of the piston forces the piston to move which in turn moves the rack. A rotary valve, typically attached to the steering shaft, supplies and meters pressurized fluid to the fluid ports to assist the vehicle operator when exerting force on the steering wheel.
In order to maintain engagement between the teeth of the pinion gear and those of the rack, such steering systems typically employ or utilize a yoke assembly to support the rack and pinion gear set. The yoke assembly typically includes a yoke, a yoke spring, a threaded yoke plug and a retention feature. The yoke transmits a load from the yoke spring to the rack to maintain engagement between the rack and pinion. The opposite end of the yoke spring contacts the yoke plug that threadably engages the housing. The yoke plug is set mechanically to ensure contact between the rack and pinion teeth. Once set, the retention feature locks the yoke plug in place.
Rack grease, which fills the rack and pinion housing cavity, seals the yoke/yoke plug assembly from the outside environment. The steering gear environment is very harsh and is subject to water, debris and other contamination. Over time, the water or other contaminants make their way to the rack and pinion housing through the yoke plug threads and rack grease causing corrosion of the steering assembly components. The corrosion typically results in excessive axial lash in the tie rods causing steering play along with noise, vibration and harshness issues. Corrosion may also cause damage to the steering assembly system seals resulting in power steering fluid loss and eventual loss of the power steering function. One known design that provides such a sealed interface includes a separate seal member between the rack and pinion housing and the yoke plug. However, this separate seal member adds costs, both production and component, to the rack and pinion steering system.
Thus, it is desirable to have a sealed yoke assembly without requiring additional components to provide the seal so as to reduce the final cost of the yoke assembly and yet provide a robustly sealed interface to protect steering gear internal components from water and other contaminants.